The field of the invention is magnetic resonance (“MR”) imaging methods and systems. More particularly, the invention relates to an MR system which correlates MR images with acquired physiological data.
When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field B0), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency. If the substance, or tissue, is subjected to a magnetic field (excitation field B1) which is in the x-y plane and which is near the Larmor frequency, the net aligned moment Mz, may be rotated, or “tipped,” into the x-y plane to produce a net transverse magnetic moment Mt. A signal is emitted by the excited spins after the excitation signal B1 is terminated. This signal may be received and processed to form an image.
When utilizing these signals to produce images, magnetic field gradients (Gx Gy and Gz) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used. The resulting set of received signals are digitized and processed to reconstruct the image using one of many well-known reconstruction techniques.
A magnetic resonance imaging (“MRI”) system which processes and reconstructs such signals may be offered with a range of polarizing magnetic strengths and configurations. The MRI system may also be offered with a range of different optional features such as magnetic resonance angiography (“MRA”), cardiac imaging and functional magnetic resonance imaging (“fMRI”). Despite such differences, all MRI systems include an operator interface which enables a particular image acquisition to be prescribed, a data acquisition apparatus which uses the MR imaging modality to acquire data from a subject, an image reconstruction processor for reconstructing an image using acquired data, storage apparatus for storing images and associated patient information and an image display apparatus. A specific hardware component is provided to carry out each of these functions and software is designed and written for each hardware configuration.
With new real time clinical applications, the importance of being able to correlate physiological data such as electrocardiogram signals (“ECG”), electroencephalogram signals (“EEG”), evoked potential signals or sensory excitation signals used in functional imaging studies to MRI images has been recognized. In the area of cardiac imaging, there is also a need to correlate an MRI image to the specific part of the cardiac cycle that the image came from so that a physician can determine whether appropriate heart function is occurring. Currently, there are no MRI systems with built-in hardware and software to provide this visual correlation. Visual correlation between physiological signals and MR images is expected to enhance clinical utility of the MRI scanner.